The Argentina World Cup champion's desire to return to the Spanish club where he achieved great success has been widely documented.
Nevertheless, according to Mundo Deportivo, in order for the transfer to be approved, the 35-year-old must agree to a few non-negotiable terms.
The first is that if he must return to Camp Nou, Messi will have to accept a smaller role in the team.
Second, because the Catalan giants are not in the finest financial situation, Messi will also need to accept a lesser weekly salary.
Thirdly, if he returns to his former club, the seven-time Ballon d'Or winner, who is rumoured to have a cold relationship with club president Joan Laporta, won't demand the captaincy.
Messi will have to recognise Ronald Araujo, Marc-Andre ter Stegen, and Robert Lewandowski as the team's leaders.